1. Field of Invention
This invention relates to the field of automatic gate openers. More specifically, the invention comprises a mechanical clutch linkage which allows a user to disengage the drive mechanism of an automatic slide gate so that the gate may be opened manually.
2. Description of Prior Art
Numerous mechanisms have been patented for the operation of automatic gates. Examples are U.S. Pat. No. 5,720,132 to Renner et. al. (1998), U.S. Pat. No. 4,520,592 to Holloway (1985), and U.S. Pat. No. 4,416,085 to Lybecker et. al. (1983). Examples of patents more specifically addressing the operation of slide gates are U.S. Pat. No. 5,076,012 to Richmond et. al. (1991) and U.S. Pat. No. 4,791,757 to Orlando (1988).
Slide gates are typically used to secure parking lots for factories, offices, apartments, and the like. Security is often a prime concern. The main reason for installing a slide gate is to prevent access by unauthorized persons. Most slide gates used for these purposes are electrically operated. A competent design must therefore account for the possibility of power failure.
When the power fails, it must still be possible to open an electrically operated slide gate in order to account for emergency entrance and exit. Yet, since preventing unauthorized access to the secured area is the very reason for installing the gate to begin with, it must not be possible to open the gate from the outside simply by defeating the power supply. Various methods have been employed to address this problem. The invention described in '757 uses a release latch to disengage the driving chain from the sliding gate, identical to the release mechanism found on most overhead garage door openers. The release is triggered by a handle on the end of a short rope lanyard. Unfortunately, this method may easily be defeated by a thief reaching through the gate from the outside. Thus, it is not very secure.
A second approach is described in U.S. Pat. No. 5,076,012 to Richmond (199). The Richmond specification explains how most slide gate mechanisms use an electric motor delivering power through reduction gears. The final drive ratio is often as high as 100 to 1. If power is lost and an attempt is made to move the gate manually, the reduction gears are driven in reverse. There is therefore a very large resistance to moving the gate, and often the gate may not be moved at all. The Richmond invention addresses this recognized problem by placing a "freewheeling" or one-way clutch between the motor output and the gate drive mechanism. If torque is applied by the motor, this one-way clutch engages and transmits the torque to the gate driving mechanism. If, however, the gate is moved while the motor is stationary, the one-way clutch disengages and allows the gate to move without transferring torque to the motor. Thus, it is possible to move the gate without driving the motor.
One problem with the Richmond device is that the action of the one-way clutch renders the gate very easy to open from the outside. This problem is remedied through the use of an electrical sensing circuit and complex motor controls. If the device senses that the gate is in motion when there is no power driving the motor, then the device will energize the motor and apply a closing force to the gate. Of course, during a power failure the device is rendered completely inoperable. Thus, during a power failure, the gate may be easily pushed open. It is therefore possible to defeat the security of the Richmond device by cutting the power to the installation and pushing the gate open from the outside.
The known methods for driving the opening and closing of an automatic slide gate are therefore limited in that the security provided by the device may be defeated by either reaching through the gate to release the driving mechanism or cutting power to the installation.